WM8750JL
Production Data
OUT3 OUTPUT
The OUT3 pin can drive a 16 or 32 headphone or a line output or be used as a DC reference for a
headphone output (see Headphone Output section). It can be selected to either drive out an inverted
ROUT1 or inverted MONOOUT for e.g. an earpiece drive between OUT3 and LOUT1 or differential
output between OUT3 and MONOOUT. OUT3 can also drive an un-inverted ROUT1 signal, which
originates at the right mixer output before the output PGA.
OUT3SW selects the mode of operation required.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
00
DESCRIPTION
R24 (18h)
8:7
OUT3SW
[1:0]
OUT3 select
00 : VREF
Additional
Control (2)
01 : ROUT1 signal (volume controlled by
ROUT1VOL)
10 : MONOOUT
11 : right mixer output (no volume
control through ROUT1VOL)
Table 28 OUT3 Select
ENABLING THE OUTPUTS
Each analogue output of the WM8750JL can be separately enabled or disabled. The analogue mixer
associated with each output is powered on or off along with the output pin. All outputs are disabled by
default. To save power, unused outputs should remain disabled.
Outputs can be enabled at any time, except when VREF is disabled (VR=0), as this may cause pop
noise (see “Power Management” and “Applications Information” sections)
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
R26 (1Ah)
6
LOUT1
0
0
0
0
0
0
LOUT1 Enable
Power
Management
(2)
5
4
3
2
1
ROUT1
LOUT2
ROUT2
MONO
OUT3
ROUT1 Enable
LOUT2 Enable
ROUT2 Enable
MONOOUT Enable
OUT3 Enable
Note: All “Enable” bits are 1 = ON, 0 = OFF
Table 29 Analogue Output Control
Whenever an analogue output is disabled, it remains connected to VREF (pin 20) through a resistor.
This helps to prevent pop noise when the output is re-enabled. The resistance between VREF and
each output can be controlled using the VROI bit in register 27. The default is low (1.5k), so that any
capacitors on the outputs can charge up quickly at start-up. If a high impedance is desired for
disabled outputs, VROI can then be set to 1, increasing the resistance to about 40k.
REGISTER
ADDRESS
BIT
LABEL
VROI
DEFAULT
DESCRIPTION
R27 (1Bh)
6
0
VREF to analogue output resistance
Additional (1)
0: 1.5 k
1: 40 k
Table 30 Disabled Outputs to VREF Resistance
HEADPHONE SWITCH
The RINPUT3/HPDETECT pin can be used as a headphone switch control input to automatically
disable the speaker output and enable the headphone output e.g. when a headphone is plugged into
a jack socket. In this mode, enabled by setting HPSWEN, HPDETECT switches between headphone
and speaker outputs (e.g. when the pin is connected to a mechanical switch in the headphone socket
to detect plug-in). The HPSWPOL bit reverses the pin’s polarity. Note that the LOUT1, ROUT1,
LOUT2 and ROUT2 bits in register 26 must also be set for headphone and speaker output (see Table
31 and Table 32).
PD, April 2012, Rev 4.1
34
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
